Was it mainly Network SouthEast that installed them? Regional Railways did at Winsford, Hartford and Acton Bridge although those ones aren't there anymore but are/were there any other northern stations that had them? EMT installed one at Spondon which may still work (same as the SWT ones). Somebody uphread posted the serial number database and they were mostly south east stations.
Update: Found a map here of course it hasn't been updated.
https://pert.is/Map
Regional Railways/Central Trains installed them around Birmingham and West Midlands. These then got moved outwards to stations on the Shrewsbury line and others by London Midland.
EMT had modern versions installed as part of the EM urban penalty fare scheme. If I remember rightly the only one remaining is at Spondon though permanently out of use.
There were also machines at Attenborough, Duffield, Barrow, Sileby and maybe Syston (the memory is starting to go a bit foggy - can't remember if Syston just went straight to a full TVM).
They were an absolute pain in the proverbial as a conductor. I was trained to work pay train lines and to this day I can quick happily knock out multiple tickets in a minute. They slowed you down. You had to get the little ticket off the passenger, look at what had been paid, which could be anything from 5p to several pounds, manually deduct it in your mind from the fare for cash or give them the value of the PERTIS back in cash if they wanted to pay card, and then at the end of the shift fish them out of every pocket you had and add them up and pay them in as "cash". There was a function on the Avantix machine to treat them as a voucher but it was never used as company policy because it would have taken too long.
Considering at the time the revenue protection team hardly ever worked those trains it was a huge amount of effort for practically no reward except someone having to go and collect a load of what were mostly 5ps every week from the machines.